public IList<IList<int>> LevelOrder(TreeNode root)
{
IList<IList<int>> result = new List<IList<int>>();
if (root == null)
return result;
Queue<TreeNode> queue = new Queue<TreeNode>();
queue.Enqueue(root);
while (queue.Count > 0)
{
IList<int> items = new List<int>();
int size = queue.Count;
for (int i = 0; i < size; i++)
{
TreeNode node = queue.Dequeue();
items.Add(node.val);
if (node.left != null)
queue.Enqueue(node.left);
if (node.right != null)
queue.Enqueue(node.right);
}
result.Add(items);
}
return result;
}
//非递归版本
/*
* 对于任一结点P：
* 1)若其左孩子不为空，则将P入栈并将P的左孩子置为当前的P，然后对当前结点P再进行相同的处理；
* 2)若其左孩子为空，则取栈顶元素并进行出栈操作，访问该栈顶结点，然后将当前的P置为栈顶结点的右孩子；
* 3)直到P为NULL并且栈为空则遍历结束
*/
public IList<int> InorderTraversal2(TreeNode root)
{
IList<int> result = new List<int>();
if (root == null)
return result;
Stack<TreeNode> stack = new Stack<TreeNode>();
TreeNode current = root;
while (current != null || stack.Count > 0)
{
while (current != null)
{
stack.Push(current);
current = current.left;
}
if (stack.Count > 0)
{
current = stack.Pop();
result.Add(current.val); //访问节点
current = current.right;
}
}
return result;
}
public bool HasPathSum(TreeNode root, int sum)
{
if (root == null)
return false;
return dfs(root, root.val, sum);
}
private List<TreeNode> generateTrees(int left, int right)
{
List<TreeNode> trees = new List<TreeNode>();
if (left > right)
{
trees.Add(null);
return trees;
}
for (int i = left; i <= right; i++)
{
List<TreeNode> leftTrees = this.generateTrees(left, i - 1); //左子树可能性
List<TreeNode> rightTrees = this.generateTrees(i + 1, right); //右子树可能性
//构建以i为根的树
for (int j = 0; j < leftTrees.Count; j++)
{
for (int k = 0; k < rightTrees.Count; k++)
{
TreeNode currentTree = new TreeNode(i);
currentTree.left = leftTrees[j];
currentTree.right = rightTrees[k];
trees.Add(currentTree);
}
}
}
return trees;
}
public void OJ114_FlattenBinaryTreeToLinkedListTest1()
{
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
root.left.left = new TreeNode(3);
root.left.right = new TreeNode(4);
root.right = new TreeNode(5);
root.right.right = new TreeNode(6);
new OJ114_FlattenBinaryTreeToLinkedList().Flatten(root);
Assert.AreEqual(1, root.val);
Assert.AreEqual(null, root.left);
Assert.AreEqual(2, root.right.val);
Assert.AreEqual(null, root.right.left);
Assert.AreEqual(3, root.right.right.val);
Assert.AreEqual(null, root.right.right.left);
Assert.AreEqual(4, root.right.right.right.val);
Assert.AreEqual(null, root.right.right.right.left);
Assert.AreEqual(5, root.right.right.right.right.val);
Assert.AreEqual(null, root.right.right.right.right.left);
Assert.AreEqual(6, root.right.right.right.right.right.val);
}
public bool IsSymmetric(TreeNode root)
{
if (root == null)
return true;
return isSymmetric(root.left, root.right);
}
public int MinDepth(TreeNode root)
{
if (root == null)
return 0;
this.dfs(root, 1);
return minDepth;
}
public IList<IList<int>> ZigzagLevelOrder(TreeNode root)
{
IList<IList<int>> result = new List<IList<int>>();
if (root == null)
return result;
Queue<TreeNode> queue = new Queue<TreeNode>();
queue.Enqueue(root);
bool isReverse = false;
while (queue.Count > 0)
{
List<int> arr = new List<int>();
int size = queue.Count;
for (int i = 0; i < size; i++)
{
TreeNode node = queue.Dequeue();
arr.Add(node.val);
if (node.left != null)
queue.Enqueue(node.left);
if (node.right != null)
queue.Enqueue(node.right);
}
if (isReverse)
arr.Reverse();
isReverse = !isReverse;
result.Add(arr);
}
return result;
}
public IList<IList<int>> LevelOrderBottom(TreeNode root)
{
IList<IList<int>> result = new List<IList<int>>();
if (root == null)
return result;
Stack<IList<int>> stack = new Stack<IList<int>>();
Queue<TreeNode> queue = new Queue<TreeNode>();
queue.Enqueue(root);
while (queue.Count > 0)
{
IList<int> items = new List<int>();
int num = queue.Count;
for (int i = 0; i < num; i++)
{
TreeNode node = queue.Dequeue();
items.Add(node.val);
if (node.left != null)
queue.Enqueue(node.left);
if (node.right != null)
queue.Enqueue(node.right);
}
stack.Push(items);
}
while (stack.Count > 0)
result.Add(stack.Pop());
return result;
}
public void OJ129_SumRootToLeafNumbersTest1()
{
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
int sum = new OJ129_SumRootToLeafNumbers().SumNumbers(root);
Assert.AreEqual(25, sum);
}
public void OJ098_ValidateBinarySearchTreeTest2()
{
TreeNode root = new TreeNode(1);
root.right = new TreeNode(1);
bool result = new OJ098_ValidateBinarySearchTree().IsValidBST(root);
Assert.AreEqual(false, result);
}
public void OJ124_BinaryTreeMaximumPathSumTest1()
{
TreeNode tree = new TreeNode(1);
tree.left = new TreeNode(2);
tree.right = new TreeNode(3);
int result = new OJ124_BinaryTreeMaximumPathSum().MaxPathSum(tree);
Assert.AreEqual(6, result);
}
public IList<IList<int>> PathSum(TreeNode root, int sum)
{
if (root == null)
return result;
this.dfs(root, root.val, new List<int>() { root.val }, sum);
return result;
}
public void OJ094_BinaryTreeInorderTraversalTest1()
{
TreeNode tn = new TreeNode(1);
tn.right = new TreeNode(2);
tn.right.left = new TreeNode(3);
IList<int> result = new OJ094_BinaryTreeInorderTraversal().InorderTraversal2(tn);
ArrayAssert.AreEqual(new int[] { 1, 3, 2 }, result.ToArray());
}
public void OJ111_MinimumDepthOfBinaryTreeTest2()
{
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
int result = new OJ111_MinimumDepthOfBinaryTree().MinDepth(root);
Assert.AreEqual(2, result);
}
private void inorderTraversal(TreeNode root, IList<int> result)
{
if (root == null)
return;
this.inorderTraversal(root.left, result);
result.Add(root.val);
this.inorderTraversal(root.right, result);
}
public void RecoverTree(TreeNode root)
{
this.inOrder(root);
int temp = p.val;
p.val = q.val;
q.val = temp;
}
private int getTreeHeight(TreeNode root)
{
if (root == null)
return 0;
int leftHeight = this.getTreeHeight(root.left);
int rightHeight = this.getTreeHeight(root.right);
return Math.Max(leftHeight, rightHeight) + 1;
}
public void OJ112_PathSumTest2()
{
TreeNode root = new TreeNode(5);
root.left = new TreeNode(4);
root.right = new TreeNode(6);
bool result = new OJ112_PathSum().HasPathSum(root, 9);
Assert.AreEqual(true, result);
}
public void inOrderTraversal(TreeNode node)
{
if (node == null)
return;
inOrderTraversal(node.left);
list.Add(node.val);
inOrderTraversal(node.right);
}
public IList<int> InorderTraversal(TreeNode root)
{
IList<int> result = new List<int>();
if (root == null)
return result;
inorderTraversal(root, result);
return result;
}
public bool IsSameTree(TreeNode p, TreeNode q)
{
if (p == null && q == null)
return true;
else if (p == null || q == null)
return false;
return p.val == q.val
&& IsSameTree(p.left, q.left)
&& IsSameTree(p.right, q.right);
}
private TreeNode generateBST(int[] nums, int left, int right)
{
if (left > right)
return null;
int mid = (left + right) / 2;
TreeNode node = new TreeNode(nums[mid]);
node.left = this.generateBST(nums, left, mid - 1);
node.right = this.generateBST(nums, mid + 1, right);
return node;
}
public void OJ101_SymmetricTreeTest2()
{
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
root.left.right = new TreeNode(3);
root.right = new TreeNode(2);
root.right.right = new TreeNode(3);
bool result = new OJ101_SymmetricTree().IsSymmetric(root);
Assert.AreEqual(false, result);
}
public void OJ104_MaximumDepthOfBinaryTreeTest1()
{
TreeNode root = new TreeNode(3);
root.left = new TreeNode(9);
root.right = new TreeNode(20);
root.right.left = new TreeNode(15);
root.right.right = new TreeNode(7);
int result = new OJ104_MaximumDepthOfBinaryTree().MaxDepth(root);
Assert.AreEqual(3, result);
}
public void OJ098_ValidateBinarySearchTreeTest1()
{
TreeNode root = new TreeNode(5);
root.left = new TreeNode(3);
root.right = new TreeNode(8);
root.right.left = new TreeNode(6);
root.right.right = new TreeNode(10);
bool result = new OJ098_ValidateBinarySearchTree().IsValidBST(root);
Assert.AreEqual(true, result);
}
public void OJ110_BalancedBinaryTreeTest1()
{
TreeNode root = new TreeNode(3);
root.left = new TreeNode(9);
root.left.left = new TreeNode(9);
root.right = new TreeNode(20);
root.right.left = new TreeNode(15);
root.right.right = new TreeNode(7);
bool result = new OJ110_BalancedBinaryTree().IsBalanced(root);
Assert.AreEqual(true, result);
}
private bool isSymmetric(TreeNode t1, TreeNode t2)
{
if (t1 == null && t2 == null)
return true;
else if (t1 == null || t2 == null)
return false;
if (t1.val != t2.val)
return false;
return isSymmetric(t1.left, t2.right) && isSymmetric(t1.right, t2.left);
}
private int dfs(TreeNode node, int sum)
{
if (node == null)
return 0;
sum = sum * 10 + node.val;
if (node.left == null && node.right == null)
return sum;
int left = dfs(node.left, sum);
int right = dfs(node.right, sum);
return left + right;
}
private bool dfs(TreeNode root, int currentSum, int resultSum)
{
if (root.left == null && root.right == null && currentSum == resultSum)
return true;
if (root.left != null && this.dfs(root.left, currentSum + root.left.val, resultSum))
return true;
if (root.right != null && this.dfs(root.right, currentSum + root.right.val, resultSum))
return true;
return false;
}